1. Field of the Invention
The present invention relates to a process for the correction of the longitudinal registration error of a rotary printing press with several inking systems in which a control unit adjusts the desired application line of the printing plate on the material web lying on one of the two rollers by controlling the drive or drives of the two rollers directly involved in the printing process of an inking system, so that the two rollers have, at least during a period of time, a different circumferential speed.
2. Description of the Related Art
The printing of multi-color print images with rotary printing presses is done, as a rule, by the print substrate running through various inking systems in sequence, each of said inking systems imparting one color so that the multi-color print image arising arises as an overlay of several print images. Great importance is attached to the precision with which this layering is performed. Shifts of the various print images with respect to one another in the printing direction are called longitudinal registration errors. The deviations called longitudinal registration errors or the circumferential registration errors are, as a rule, corrected by the press operator at the beginning of the printing process by the press operator controlling the relative position of so-called registration marks that are applied by the various inking systems. However, this process has the disadvantage of a long reaction time and the large number of rejects associated therewith.
Thus, DE 195 27 199 proposes, in reference to a flexographic printing press, to register the registration marks with recognition sensors during the entire printing process, to supply the results of the measurement of the sensors to a control and computer unit, and to perform the longitudinal registration correction by the print cylinder being run, at least for a short period of time, at a different circumferential speed than the impression cylinder.
In the application of the process sketched in DE 195 27 199 for the correction of the longitudinal registration error during the entire printing process, it is, however, required that said optical recognition sensors monitor the print image long-term, supply the control unit with measurement signals, whereupon the same performs the control of the speed of the various print rollers necessary for the registration correction.
This process requires, therefore, among other things, a long-term optical monitoring of the print image.